Coil collapse

The total number of cross-links per gram is directly proportional to radiation dose. Either RSMW or JRg(Mw)2/3 should be independent of initial molecular weight, depending on whether all repeating units or only those near the surface of the coils have equal probabilities for intermolecular cross-link formation. Complete coil collapse is clearly ruled out by the results. Moreover, detailed calculations (46) show that a trend in the product RgMw due to systematic differences in intramolecular cross-linking, should be observed even for only partially collapsed random coils. If the coil radii in bulk polystyrene were reduced by even as much... 

After having discussed the influence of the inert salt level on the Ca2+ induced coil collapse, we would like to draw attention to another interesting aspect. As found by Michaeli [25] and confirmed by our own data [75,76], addition of inert salt increases the solubility of CaPA. This immediately poses the question of how the addition of inert salt affects the size and shape of a collapsed NaPA chain. 

Characterization. All measurements were carried out with dried specimens (particles or sheets). It is established that the thickness of the water-loaded polymer layer is higher than in the dried state, because dried polymer coils collapse [21], The amount of polymer, however, is not changed after the drying process. Thus an average equilibrium state is always measured. 

As the segment density p increases from the dilute limit (or as coils collapse for v < 0), higher-order interactions (three-body, four-body,...) become important. The fraction of space excluded by chains may be expressed by the... 

Equations (2.2.12)-(2.2.14) define the so-called random Gaussian globule resulting from coil collapse in words, all the long-range mean-square distances with Ic > J are equal, whereas those between relatively close atoms... 

Block-Type Brushes by Sequential Polymerization The sequential hving polymerization of two macromonomers or a macromonomer with a conventional comonomer forms either block-block- or block-coil-type brush structures. For example, giant rod-coil amphiphilic block copolymer bmshes were prepared via a stepwise metallocene-catalyzed polymerization [58]. In the first step, a concentrated solution of methacryloyl end-functionalized PS macromonomer (DP = 18.3, MWD = 1.05) was polymerized by the organosamarium(iii) catalyst in THF. After PS macromonomer was completely consumed, the active center remained living, and tert-butyl methacrylate tert-butyl methacrylate (tBMA) as a comonomer was added to grow the second block. After termination by ethanol, the poly(tert-butyl methacrylate) (PtBMA) coil block was hydrolyzed into a hydrophihc block, poly(methacrylic acid) (PMAA). The final product consisted of a hydrophobic PS brush block and a hydrophihc PMAA coil. The hydrophilic PMAA coil collapsed in nonpolar solvents, which forced the block-coil CPBs to self-assembled into giant micelles with PMAA as the core component and the stiff PS brush block as the shell to stabihze the micelles. 

Reprinted from Polymer, Volume 33, B. Wandelt, D.J.S. Birch, R.E. Imhof, R.A. Pethrick, Time-resolved excimer fluorescence studies as a probe of the coil collapse transition and phase separation in isotactic PS/BA gel, 3561, copyright 1992, with... 

Above this temperature the coil expands and below this temperature the coil collapses with concomitant macroscopic phase separation. 

For thermodynamically good solvents, the scaling exponent vcoii has a value of vcou = 3/5 that can also be calculated in the framework of a simple scaling model.For bad solvents, the coil collapses which leads to vcou < 0.5. For vcoii = = 0.5, the... 

Working in very dilute solution the dimensional changes with temperature of the polystyrene coil in a poor solvent, cyclohexane, have been studied. Two domains are recognized one (the 0-region) where R is independent of the reduced temperature t [t = (T— 0)/O] in the second the coil collapses and R t -i/ in accordance with predicted behaviour. This system has been studied further in the region of the lower critical solution temperature (LCST), that is near the solvent critical point. The temperature range was 70— 220 °C and in this r on Edwards equation is modified to ... 

Fig. 7.39. Expansion of polydimethylsiloxane (PDMS) in supercritical CO2 above the theta temperature T 55 °C). Below T , diverging fluctuations in concentration prevent the coil collapse observed in organic (e.g. cyclohexane see Fig. 7.38) soivents. (Reproduced with permission from [239]. Copyright 1999 American Chemical Society.)...

Figure 6. Expansion of PDMS chains in SC CO2 above the temperature Tg 65 °C. Below Tg, diverging concentration fluctuations prevent the coil collapsing as observed in organic solvents. The inset illustrates first observation of a pressure in solutions of PDMS in SC CO2. As observed in organic solvents, the polymer chains do not collapse below Pg.

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